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ABSTRACT

Seventy-seven species of smaller calcareous foraminifers belonging to thirty-two genera and fourteen families, and two groups of uncertain affinity are distinguished in Mississippian and Lower Pennsylvanian strata from four localities in southern and eastern Nevada. Most belong to the Superfamily Endothyraceae, a group characterized by skew, planispiral, or erect growth, a simple or cribrate aperture, and a layered wall of secreted calcite. Five new species are named.

The Mississippian foraminifers permit recognition of assemblage zones based on the global zonation scheme of Bernard Mamet. The Pennsylvanian strata are not zoned.

Formations studied in the Arrow Canyon Range, north-central Clark County, include the Crystal Pass Limestone, Dawn Limestone, Anchor Limestone, Bullion Limestone, Yellowpine Limestone, Battleship Wash Formation, Indian Springs Formation, and the lower part of the Bird Spring Formation. The Joana Limestone was studied southwest of Ely, Nevada, at Ward Mountain in the Egan Range, and the lower part of the exposed Ely Limestone was studied northwest of Ely in the vicinity of the Moorman Ranch and in the Butte Mountains.

The upper part of the Crystal Pass Limestone in the Arrow Canyon Range contains foraminifers that appear to be late Kinderhook in age, but the lower beds lack stratigraphically useful foraminifers. The entire formation has been previously assigned to the Late Devonian on the basis of conodont assemblages. The Dawn Limestone which disconformably overlies the Crystal Pass Limestone is early and middle, and, possibly, late Osage in age. The successively overlying Anchor and Bullion Limestones contain only sparse, nondiagnostic foraminifers, but, based on their stratigraphic position, they are late Osage to middle Meramec. The overlying Yellowpine Limestone and the lower beds of the Battleship Wash Formation contain a well developed middle and late Meramec fauna; however, the upper part of the Battleship Wash is middle to late Chester with no evidence of an intervening early Chester fauna. The Indiana Springs Formation and the lowest part of the overlying Bird Spring Formation are late Chester. The remainder of the Bird Spring that was measured was deposited in Morrow time.

At Ward Mountain the lower member of the Joana Limestone has a late Kinderhook fauna. The upper member is Osage in age.

Foraminifers are scarce in the lower part of the exposed Ely Limestone at the Moorman Ranch and Butte Mountains sections. The microfaunal associations suggest a Morrow age for these rocks.

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